To clarify Hopeandchange
A shotgun must have left the factory with a pistol grip and never had stock installed to be a AOW. If it is registered as a AWO it may never have a stock installed later on.
If you the OP wants to have a pistol grip and a full length stock all that is required by the ATF is that the gun be able to be readily restored to it's length stated on the form 1.
"9mm has a very long history of being a pointy little bullet moving quickly" --Sevens